Relevance: A recent NIOSH review of Mine Safety and Health Administration accident and fatality reports for underground metal/nonmetal mines showed that nearly one-quarter of all fatalities at such mines were related to rock falls. About one third of these fatalities involved scaling. A significant number of lost time injuries also occur during scaling loose and fragmented rock from the periphery of underground workings. Description: The objective of this research will be to evaluate the effectiveness of using high-pressure waterjet technology as part of a mechanized scaling system to safely remove loose and unstable rock from underground mine openings. This proposed project will build upon previous research in waterjet scaling performed at the Colorado School of Mines Experimental Mine, where an existing prototype waterjet scaling rig and high-pressure pump will be used. The relative effectiveness of various nozzles designs, including continuous, oscillating, and two types of pulsed jets, will be examined. Pulsed jets have been shown to be dramatically more effective than continuous waterjets in a wide range of industrial cutting and cleaning applications. It is believed that the utilization of a properly designed pulsed jet system will provide significant improvements in employee safety over that of conventional manual or mechanized scaling methods by removing miners from high-risk areas and reducing their potential exposure to rock falls. Additional benefits stem from the increased efficiency of high velocity fluid to scour and displace damaged rock and substantive improvements in the performance and adhesion characteristics of shotcrete as a ground support membrane. Focal to this proposed research will be efforts to empirically quantify the critical operating variables associated with hydraulic scaling and to assess the performance and efficiency of these systems relative to conventional scaling methods in terms of employee health and safety. The project will conclude by performing an extensive field trial at an operating underground mine.